1. Field
One or more example embodiments relate to selecting a base station for handover, for example, a network element or method for selecting a base station for handover from a plurality of target base stations.
2. Description of the Related Art
A rate of successful handovers in a wireless communication system is used as a benchmark for measuring performance of the wireless communication system. This is because an unsuccessful handover leads to communication degradation for the user due to data loss or gaps or even connection loss. For real-time service such as voice and video telephony, the degradation translates to garbled voice, voice gap and dropped calls. With the introduction of wideband wireless technology, wireless data networks are gradually replacing the traditional wireless circuit network due to their relatively low cost, high bandwidth and rich multi-media services.
There are many mobile station initiated handover methods that signal the source base station, which serves the signaling mobile station, to select a target base station for handover. One such method sets up multiple target base stations simultaneously over the Radio Access Network (RAN) backbone and performs multi-casting from a data anchor to these target base stations. The purpose of this method is to achieve a relatively fast handover by avoiding sequential handover admission control on a plurality of target base stations, which occurs when the first target evaluated target base station lacks resources to serve the incoming handover and therefore one or more subsequent target base stations must be sequentially evaluated.
However, setting up and multi-casting multiple target base stations simultaneously increases the complexity of resource reservation and de-allocation and therefore the potential for handover failure. In addition, the resources, both at the multiple target base stations and over the backhaul of the RAN, are wasted by this method.
Nonetheless, setting up multiple target base stations sequentially may lead to longer handover times and/or handover failure if one or more of the sequentially setup target base stations refuses the handover.
Code division multiple access (CDMA) technology, which provides an example of setting up the multiple target base stations simultaneously, uses multiple legs, which include one or more downlink (or forward) channels for transmitting information from the base station to the mobile station and one or more uplink (or reverse) channels for transmitting information from the mobile station to the base station. 3.5G and 4G wireless technology, which is an example of setting up the multiple target base stations sequentially, uses an Orthogonal Frequency-Division Multiple Access (OFDMA) air interface technology that adopts a single serving leg, which only uses one communication link to/from the mobile station.
The single leg support makes handover evaluation even more important because a handover trigger must be accurate and allow enough handover preparation time while the communication link is still healthy since the communication link will not have the benefit of multiple leg support. Further, handover resource management must be relatively fast and robust enough to ensure the base station targeted for handover can accept the incoming handover in time.